In the field of this disclosure, stereoscopic imagery is displayed by a 3D display. 3D displays typically exploit the binocular nature of human vision by using spatial and optical arrangement of display elements so that images on a 2-dimensional display can give the illusion of “depth”, or an extra dimension into the image plane of the display. Stereoscopic imaging has many practical applications, including, for example, medical imaging, scientific visualization, virtual prototyping, and entertainment.
Most 3D display technologies provide “stereo parallax”, which is the effect that each eye sees a different view of a scene, which in turn provides a depth cue. Such displays provide a different view of a scene to each eye.
Stereoscopic 3D displays require the use of special eyewear and provide only two views, whereas autostereoscopic 3D displays do not require special eyewear for viewing. In contrast to typical stereoscopic 3D display technologies that require special eyewear, some autostereoscopic 3D displays might also provide more than two views of a scene. By way of providing more than two views of a scene, an autostereoscopic 3D display can provide another kind of depth cue called “movement parallax”. Movement parallax is the effect that a viewer sees slightly different views of an image by moving their head.
Autostereoscopic displays are ordinarily capable of displaying multiple views, either simultaneously, or sequentially over time. Autostereoscopic displays might use optics, such that each of the viewer's eyes perceives a different view of the displayed source stereoscopic image. In other words, special optical arrangement is used such that a person within a certain location with respect to the display can see only one view from each eye, and such that each eye perceives a different view of the scene. In other examples, autostereoscopic displays might use a head or eye tracking unit to determine the user's viewing position, and either alone or in combination with the use of optics such as active optics, change the displayed content of the display such that each eye receives a view that simulates stereo parallax and/or movement parallax.
Each view displayed by an autostereoscopic display is typically viewable only in a narrow range of viewing angles. These ranges of viewing angles (i.e., plural angular ranges, one each for each view) exist geometrically, regardless of the viewer. In some autostereoscopic displays, views are provided for all ranges of viewing angles regardless of whether there is a viewer. In other autostereoscopic displays, views are only provided for the ranges of viewing angles where there is a viewer.
FIG. 1 is a schematic diagram of an autostereoscopic display 1 with fixed optics using spatial multiplexing of more than one views. Fixed optics 3 (e.g., a lenticular sheet or a parallax barrier) allows a viewer to see each view of a color display pixel only in a narrow range of angles.
For example, as shown in FIG. 1, source stereoscopic imagery 4 is demultiplexed to obtain multiple views of each image frame (e.g., views 1 to 4). Autostereoscopic display 1 displays four views simultaneously, namely views one through four.
For example, optics 3 is arranged so that a viewer's eye in angular range 21 perceives view 1 of pixel 30, a viewer's eye in angular range 22 perceives view 2 of pixel 30, a viewer's eyes in angular range 23 perceives view 3 of pixel 30, and a viewer's eye in angular range 24 perceives view 4 of pixel 30. Likewise, optics 3 is arranged so that a viewer's eye in angular range 25 perceives view 1 of pixel 31, a viewer's eye in angular range 26 perceives view 2 of pixel 31, a viewer's eyes in angular range 27 perceives view 3 of pixel 31, and a viewer's eye in angular range 28 perceives view 4 of pixel 31.
Regions where certain combinations of views of pixels are visible are called viewing regions, and all of the viewing regions together comprise the whole of an operating viewing zone for the display. The geometry of the viewing regions depends on the design, e.g., optics, of the autostereoscopic display.
FIG. 1 shows multiple viewing regions. In the example illustration, the display allows a maximum of four different views (e.g., views 1 to 4). There are four viewing regions that are shaded and correspond to viewing regions where, in each one, a consistent view with good stereo parallax is seen. In other words, each shaded viewing region represents a region in which a single, consistent view of the whole image can be seen. These shaded viewing regions are optimal viewing locations for respective views, each relatively free of pseudoscopy.
Other viewing regions correspond to viewing regions where there might be an appreciable degree of pseudoscopy. For example, in one region A, both view 1 of some pixels and view 2 of some other pixels are seen, i.e., there is crosstalk among different views.
As shown in FIG. 1, and as illustrated with the location of the head of the viewer, each of the viewer's eyes fall into a viewing region of a different view, and each eye perceives a different view of the displayed image of the scene. For example, as shown in FIG. 1, the left eye perceives view 2 of the image, while the right eye perceives view 3 of the image, thus leading to a stereo parallax effect. Slight left-to-right head movement causes the eyes to move to another pair of viewing regions which provides different views, thus leading to a movement parallax effect.
The fixed optics layer 3 shown in FIG. 1 can be implemented in a number of ways. One technique is based on lenslets, where lenslets in a lenticular sheet in front of the pixels 2 refract light from the pixels such that they can be seen only in a certain range of viewing angles. Another technique for implementing the fixed optics layer is parallax barrier which is based on occlusion. Yet another variation uses parallax illumination instead of parallax barrier.
FIGS. 2A and 2B are schematic diagrams of an autostereoscopic display using active steerable optics 33 to adapt to viewer location. In the autostereoscopic display depicted in FIGS. 2A and 2B, only two views are displayed at any time. These two views are optimized based on the eye locations of the viewer, which is tracked continuously. The active optics may be implemented as steerable optical filters or, alternatively, as steerable projectors.
For example, as shown in FIGS. 2A and 2B, source stereoscopic imagery 43 is demultiplexed to obtain multiple views of each image frame (e.g., views 1 to 4). Autostereoscopic display 42 selects two views for display based on eye locations of the viewer, as determined by eye tracking unit 44.
FIG. 2A depicts the selection of views 1 and 2 based on first positions of eye locations. In FIG. 2A, optics 33 is driven so that a viewer's eye in angular range 51 perceives view 1 of pixel 40, and a viewer's eye in angular range 52 perceives view 2 of pixel 40. On the other hand, no views are visible in the angular ranges 53 and 54 since there is no viewer in those ranges.
Likewise, optics 33 is driven so that a viewer's eye in angular range 55 perceives view 1 of pixel 41, and a viewer's eye in angular range 56 perceives view 2 of pixel 41. Again, no views are visible in the angular ranges 57 and 58 since there is no viewer in those ranges.
Similar to FIG. 1, FIG. 2A shows multiple viewing regions. In the exemplary illustration, the display allows a maximum of four different views (e.g., views 1 to 4). There are four viewing regions that are shaded and correspond to viewing regions where, in each one, a consistent view relatively free of pseudoscopy is seen.
As shown in FIG. 2A, and as illustrated with the location of the head of the viewer, each of the viewer's eyes fall into a viewing region of a different view, and each eye perceives a different view of the displayed image of the scene. For example, as shown in FIG. 2A, the left eye perceives view 1 of the image, while the right eye perceives view 2 of the image, thus leading to a stereo parallax effect.
FIG. 2B depicts the result of left-to-right head movement of the viewer depicted in FIG. 2A. The left-to-right head movement is detected by eye tracking unit 44. In particular, eye tracking unit 44 detects that the viewer's left eye has moved to a viewing region from which view 3 is perceived, and the viewer's right eye has moved to a viewing region from which view 4 is perceived. In response to the detection by the eye tracking unit 44, views 3 and 4 are selected for display. Accordingly, slight left-to-right head movement causes a different pair of views to be selected for display. Thus, the slight left-to-right head movement leads to a movement parallax effect.
FIGS. 3A and 3B are schematic diagrams of an autostereoscopic display 74 using temporal multiplexing of multiple views and time switching optics 34. The autostereoscopic display 74 depicted in FIGS. 3A and 3B displays multiple views of source stereoscopic image 73 successively. In this approach, multiple views are displayed successively, one view at a time, at a high refresh rate. For example, if there are M views, and the frame rate is F frames per second, then the refresh rate of the display is typically M×F Hz. In particular, if M=9, F=120, then the refresh rate would be 1080 Hz. For example, a high speed liquid crystal display might be used to implement such an autostereoscopic display.
For example, as shown in FIGS. 3A and 3B, source stereoscopic imagery 73 is demultiplexed to obtain multiple views of each image frame (e.g., views 1 to 4). Autostereoscopic display 74 displays views 1 to 4 successively, such that only one view is displayed at a time.
FIG. 3A depicts the selection of view 1 based on a predetermined timing. In FIG. 3A, optics 34 is driven so that a viewer's eye in angular range 61 perceives view 1 of pixel 50. Likewise, optics 34 is driven so that a viewer's eye in angular range 61 perceives view 1 of pixel 51.
As shown in FIG. 3A, the viewer's left eye is located in viewing region 72, and the viewer's right eye is located in viewing region 75. Since based on timing view 1 is selected for display, view 1 of the whole image is visible in region 72, and the viewer's left eye perceives view 1. However, views 2, 3 and 4 are not visible during this time slice.
FIG. 3B depicts the selection of view 2 for display, after view 1 has been selected for display for a time of 1/(M×F) seconds. As shown in FIG. 3B, view 2 of the whole image is visible in region 75, and the viewer's right eye perceives view 2. However, views 1, 3 and 4 are not visible during this time slice. When the frame rate F is high, a viewer perceives a left image (view 1) and right image (view 2) “simultaneously” due to persistence of human vision.